Member mounting method and member assembly

ABSTRACT

A method for mounting a second member on a first member, wherein a pad layer is provided on the first member, and wherein an annular aperture portion exposing the first member to the bottom and having at least one discontinuous portion is provided in a region of the pad layer for mounting the second member having a mount face, the annular aperture portion having the same outer shape as the mount face of the second member is disclosed. The method includes: filling the aperture portion with a solder paste layer; and disposing the mount face of the second member on the solder paste layer, and melting and cooling the solder paste layer to mount the second member on the first member.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.13/367,887 filed Feb. 7, 2012, the entirety of which is incorporatedherein by reference to the extent permitted by law. The presentapplication claims the benefit of priority to Japanese PatentApplication No. JP 2011-047344 filed on Mar. 4, 2011 in the Japan PatentOffice, the entirety of which is incorporated by reference herein to theextent permitted by law.

FIELD

The present disclosure relates to methods for mounting two members, andto member assemblies configured from two members.

BACKGROUND

Construction of an optical transmission system on a printed boardrequires high-accuracy registration and anchoring of an opticalconnector that connects an element such as a semiconductor laser elementand a photodetector to a member such as an optical fiber. Typically, anaccuracy as high as about ±10 μm is needed for the light axisregistration. Taking as an example the PT optical connectors developedby The National Institute of Advanced Industrial Science and Technologyand NEC Corporation and specified in JPCA-PE03-01-06S DetailSpecification for Optical Board Connector type PT using Glass Fibres, aregistration accuracy of, for example, ±3 μm or less is required betweenthe PT guide pin, a registration pin of the PT optical connector, andthe guide hole, a registration hole provided for a PT optical module, orbetween the PT guide pin, a registration pin of a PT optical module andthe guide hole, a registration hole provided for the PT opticalconnector. Further, the optical connectors disclosed in, for example,JP-A-2011-017924, JP-A-2011-017925, JP-A-2008-046367, andJP-A-2004-184429 also use a guide pin and a guide hole for theregistration between the optical connector and a module main body orbetween the optical connectors. Further, high registration accuracy isalso often required, for example, in mounting various electroniccomponents on a printed board, or another substrate on a printed board.

SUMMARY

When the main body portion of a PT optical connector or PT opticalmodule mounting a PT guide pin is a mount substrate such as a printedboard, a designated tool such as a high-accuracy mounter is needed forthe accurate registration and mounting on the mount substrate. This isthe major cause of the high assembly cost. The same problem occurs whenmounting various electronic components or another substrate on a printedboard realized by a mount substrate.

Accordingly, it is desirable to provide a member mounting method thatenables accurate and easy mounting of two members, and a member assemblyconfigured from two members based on the member mounting method.

An embodiment of the present disclosure is directed to a method formounting a second member on a first member, wherein a pad layer isprovided on the first member, and wherein an annular aperture portionexposing the first member to the bottom and having at least onediscontinuous portion is provided in a region of the pad layer formounting the second member having a mount face, the annular apertureportion having the same outer shape as the mount face of the secondmember. The method includes: filling the aperture portion with a solderpaste layer; disposing the mount face of the second member on the solderpaste layer, and melting and cooling the solder paste layer to mount thesecond member on the first member. Note that, when filling the apertureportion with the solder paste layer, the solder paste layer may fill theaperture portion either completely or incompletely. Further, whenfilling the aperture portion with the solder paste layer, the solderpaste layer may slightly bulges beyond the aperture portion onto theedge on the pad layer to form the solder paste layer thereon.

Another embodiment of the present disclosure is directed to a memberassembly as an assembly of a first member that includes a pad layer, anda second member that has amount face. The member assembly includes anannular aperture portion in a second member-mounting region of the padlayer so as to expose the first member to the bottom and form at leastone discontinuous portion. The annular aperture portion has the sameouter shape as the mount face of the second member, and a solder pastelayer fills the aperture portion to mount the second member on the firstmember.

In the member mounting method or the member assembly of the embodimentof the present disclosure, an annular aperture portion is provided in asecond member-mounting region of the pad layer so as to expose the firstmember to the bottom and form at least one discontinuous portion (jointportion), the second member having a mount face. Further, the annularaperture portion has the same outer shape as the mount face of thesecond member. This enables the second member to be mounted on the firstmember by self-aligning with the first member, using the solder pastelayer. Further, the melting of the solder paste layer does not leave agas component at the interface between the solder paste layer and themount face of the second member, because a flux or other gas componentscontained in the solder paste layer can be released to outside via thediscontinuous portion (joint portion) formed in the annular apertureportion. The second member can thus be mounted on the first member bothaccurately and easily.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partial schematic plan view of a pad layer of a firstembodiment; FIG. 1B is a schematic partial cross sectional view of afirst member including the pad layer; FIG. 1C is a schematic partialcross sectional view of the first member including the pad layer asviewed from a different direction from that in FIG. 1B; FIG. 1D is aschematic cross sectional view of a second member.

FIG. 2A is a schematic view of the first member and other components asviewed from above; FIGS. 2B and 2C are schematic partial cross sectionalviews of the first member and other components, taken along the linesB-B and C-C in FIG. 2A.

FIGS. 3A and 3B are schematic partial end views taken along the linesC-C and B-B in FIG. 1A, explaining a member mounting method of the firstembodiment; FIG. 3C is a partial schematic plan view of the pad layerand a solder paste layer.

FIGS. 4A and 4B are a schematic partial end view and a partial crosssectional view, respectively, taken along the lines C-C and B-B in FIG.1A, explaining the member mounting method of the first embodiment as acontinuation of FIGS. 3A and 3B.

FIGS. 5A and 5B are a schematic partial end view and a partial crosssectional view, respectively, taken along the lines C-C and B-B in FIG.1A, explaining the member mounting method of the first embodiment as acontinuation of FIGS. 4A and 4B.

DETAILED DESCRIPTION

The following will describe the present disclosure based on anembodiment and example with reference to the accompanying drawings. Itshould be noted that the present disclosure is not limited to thefollowing embodiment and example, and the numerical values and materialspresented in the following embodiment and example are illustrative.Descriptions will be given in the following order.

1. Overall descriptions, including the member mounting method and memberassembly of the present disclosure 2. First Embodiment (the membermounting method and the member assembly of the present disclosure), andother

[Overall Descriptions, Including the Member Mounting Method and MemberAssembly of the Present Disclosure]

The member mounting method or member assembly according to an embodimentof the present disclosure may be configured to include a second memberthat has a mount face and a side face extending from the mount face, andthat may be made of copper, a copper alloy, aluminum, or an aluminumalloy. The side face of the second member may have a film of poor solderwettability (for example, a film with solder wettability poorer thanthat of the mount face of the second member). Note that, in this case,the mount face of the second member may have a film of good solderwettability (for example, a film with better solder wettability thanthat of the film formed on the side face of the second member).

In the member mounting method of the present disclosure including theforegoing preferred embodiment, the mount face of the second member maybe disposed on a solder paste layer, and the solder paste layer may bemelted so that the second member mounts itself on the first member byself-aligning, using the surface tension created by the melting of thesolder paste layer.

In the member mounting method or member assembly of the presentdisclosure including the foregoing preferred embodiment andconfigurations, the annular aperture portion has the same outer shape asthe mount face of the second member. As used herein, “the same outershape” encompasses a homothetic shape. Specifically, it is preferablethat, for example, 0.90<R₁/R₂<1.1 be satisfied, where R₁ is the diameterof the outer shape of the annular aperture portion, and R₂ is thediameter of the outer shape of the mount face of the second member.

Further, in the member mounting method or member assembly of the presentdisclosure including the foregoing preferred embodiment andconfigurations, the annular aperture portion may have four discontinuousportions, and the four discontinuous portions may be disposed with4-fold rotational symmetry. However, the configuration of thediscontinuous portions is not limited to this, and, for example, may besuch that there is 2-fold rotational symmetry (two discontinuousportions in the annular aperture portion), 3-fold rotational symmetry(three discontinuous portions in the annular aperture portion), or, morebroadly, N-fold rotational symmetry with N discontinuous portions in theannular aperture portion (where N is a natural number of 2 or more).Further, the discontinuous portions may be disposed with no rotationalsymmetry.

Further, in the member mounting method or member assembly of the presentdisclosure including the foregoing preferred embodiment andconfigurations, the outer shape of the annular aperture portion may becircular. However, the outer shape of the annular aperture portion isnot limited to this, and may be a triangle, a round triangle, aquadrangle, a round quadrangle, a polygon, a round polygon, anellipsoid, or a series of block shapes or small circles arranged on avirtual circumference of the aperture portion. The inner shape of theannular aperture portion may be homothetic to the outer shape. However,the inner shape of the annular aperture portion is not limited to this,and the annular aperture portion may have essentially any inner shape.

Further, in the member mounting method or member assembly of the presentdisclosure including the foregoing preferred embodiment andconfigurations, the portion of the first member exposed to the bottom ofthe aperture portion may be a copper layer (or a copper foil), or anickel layer formed on a copper layer (or a copper foil). However, thematerial is not limited to this, and any material may be used, as longas it can be bonded to the solder paste layer. Note that the firstmember except for the portion exposed to the bottom of the apertureportion may have any configuration, including, for example, varioustypes of printed boards and printed circuit boards, and substrates.

Further, in the member mounting method or member assembly of the presentdisclosure including the foregoing preferred embodiment andconfigurations, the mount face of the second member may be formed usingmaterials having good solder wettability and solderability, such ascopper, a copper alloy, aluminum, an aluminum alloy, gold, and platinum.Further, the second member may be formed using a plastic material (forexample, engineering plastic material) having heat resistance that canwithstand the melting temperature of the solder paste layer, and ametallic or alloy layer of copper, a copper alloy, aluminum, or analuminum alloy may be formed on the mount face of the second member.Solder wettability can be evaluated by, for example, solder contactangle measurements, or cross section analysis of the bonded interface.Solder wettability is determined as desirable when the contact angle issmall, or when an alloy is formed with the solder at the bondedinterface. Solder wettability is determined as poor when the contactangle is large, or when there is no alloy formation.

Further, in the member mounting method or member assembly of the presentdisclosure including the foregoing preferred embodiment andconfigurations (hereinafter, also referred to collectively as simply“the present disclosure”), the outer shape of the aperture portioncrosses the discontinuous portions (joint portions). The space with theshape of the inside of the annular aperture portion is occupied by aportion of the pad layer, and the discontinuous portions (jointportions) are also configured from a portion of the pad layer.

The first member of the present disclosure may be, for example, the mainbody portion of the PT optical connector or PT optical module specifiedin JPCA-PE03-01-065 Detail Specification for Optical Board Connectortype PT using Glass Fibres. The second member of the present disclosuremay be, for example, the PT guide pin (registration pin) of the PToptical connector or PT optical module. Aside from these non-limitingexamples, other examples of the first member of the present disclosureinclude the main body portion of various types, configurations, andforms of optical connectors; the main body portion of various types,configurations, and forms or optical modules; various printed boards andprinted circuit boards, and substrates; various display devices,including liquid crystal display devices, organic electroluminescence(organic EL) display devices, and electrophoretic display devices;various electronic components such as switches and sensors; andmechanical components. Other examples of the second member of thepresent disclosure include a registration pin to be mounted to the mainbody portion of various types, configurations, and forms of opticalconnectors, a registration pin to be mounted to the main body portion ofvarious types, configurations, and forms of optical modules; aregistration pin to be mounted to various printed boards and printedcircuit boards, substrates, and various types of display devices andelectronic components; and a mechanical component main body thatrequires inexpensive and accurate registration. Examples of componentsand articles used for mounting the member assembly of the first memberand the second member using the second member for registration includePT optical connectors, PT optical modules, various types,configurations, and forms of optical connectors, various types,configurations, and forms of optical modules, various printed boards,printed circuit boards, and substrates, and various display devices andelectronic components. The pad layer may be realized by, for example, aphotosensitive resin layer, or a photosensitive resin sheet or film,specifically a photosensitive polyimide film. The pad layer provided onthe first member may be provided in at least a part of the first member.The solder paste layer may be formed using a known solder paste.

First Embodiment

The first embodiment relates to the mounting method of the two membersof the present disclosure, and to the member assembly configured fromthe two members. In the first embodiment, a first member 10 is the mainbody portion of the PT optical connector specified in JPCA-PE03-01-06SDetail Specification for Optical Board Connector type PT using GlassFibres. A second member 30 is the PT guide pin (registration pin) of thePT optical connector. FIG. 1A illustrates a partial schematic plan viewof the pad layer of the first embodiment. FIG. 1B is a schematic partialcross sectional view of the first member including the pad layer, takenalong the line B-B in FIG. 1A. FIG. 1C is a schematic partial crosssectional view of the first member including the pad layer, taking alongthe line C-C in FIG. 1A. FIG. 1D is a schematic cross sectional view ofthe second member. FIG. 2A shows a schematic illustration of the firstmember and other components as viewed from above. FIGS. 2B and 2C areschematic partial cross sectional views of the first member and othercomponents, taken along the lines B-B and C-C in FIG. 2A.

The member assembly of the first embodiment is a member assembly thatincludes the first member 10 provided with a pad layer 20, and thesecond member 30 that has a mount face 32. The pad layer 20 has anannular aperture portion 21 in a region where the second member 30 ismounted. The annular aperture portion 21 exposes the first member 10 tothe bottom, and has at least one discontinuous portion (joint portion)22. The annular aperture portion 21 has the same outer shape as themount face 32 of the second member 30. The second member 30 is mountedon the first member 10 with a solder paste layer 40 applied tosubstantially the whole surface of the aperture portion 21. In the firstembodiment, the annular aperture portion 21 has four discontinuousportions 22, and these four discontinuous portions 22 are disposed with4-fold rotational symmetry. Specifically, the discontinuous portions 22are disposed at the 0 o'clock, 3 o'clock, 6 o'clock, and 9 o'clockpositions of the annular aperture portion 21 as viewed from the centerof the discontinuous portions 22. The annular aperture portion 21 has acircular outer shape, and the inner shape thereof is also circular,homothetic to the outer shape. The space 23 with the shape of the insideof the annular aperture portion 21 is occupied by a portion of the padlayer (shown as a pad layer center region 24), and the discontinuousportions 22 are also configured from portions of the pad layer. Theouter shape and inner shape of the aperture portion 21 cross thediscontinuous portions 22.

The first member 10, specifically the base material 11 as the main bodyportion of the PT optical connector is fabricated from, for example, aheat-resistant resin, and includes, as illustrated in FIG. 2C, anoptical fiber anchoring unit 14 that anchors an optical fiber 50, and areflecting mirror 15 that creates a 90° angle with the travel directionof the light rays that emerges from the optical fiber 50, or of theincident rays that fall on the optical fiber 50. A copper layer 12 and anickel layer 13 are formed by plating in a portion of the first member(main body portion of the PT optical connector) 10, and the pad layer 20of 25 μm-thick photosensitive polyimide resin is formed over theselayers 12 and 13. The portion of the first member 10 exposed to thebottom of the aperture portion 21 provided in the pad layer 20 isconfigured from, for example, the copper layer 12 (thickness of 12.5 μm)and the nickel layer 13 (thickness of 3 μm) formed on the copper layer12. Note that the nickel layer 13 is formed by plating on the copperlayer 12 exposed to the bottom of the aperture portion 21.Alternatively, a gold layer may be formed on the nickel layer 13 byplating, or the nickel layer may not be formed.

The second member 30 as the PT guide pin has a side face 33 that extendsfrom the mount face 32. The mount face 32 of the second member 30 isformed, using, for example, copper. Specifically, the second member 30is made from copper. More specifically, the second member 30 isconfigured from a columnar lower member 31 and a columnar upper member34, and formed as one unit in the shape of a hat. The bottom surface ofthe columnar lower member 31 corresponds to the mount face 32, and theside face of the columnar lower member 31 corresponds to the side face33 that extends from the mount face 32. Further, a film 35 of poorsolder wettability, specifically, a titanium film (thickness of 0.1 μm),or a heat-resistant coating film (for example, thickness of about 10 μm)is formed on the side face 33 of the second member 30 (specifically, inportions where solder wetting needs to be prevented, more specifically,on the whole surface of the second member 30 except the mount face 32,or on the side face 33 or the lower portion of the side face 33).

In the first embodiment, a PT optical module 60 is used as the componentused for mounting the member assembly of the first member 10 and thesecond member 30 using the second member 30 for registration. The secondmember 30 is fitted to a guide hole 62 provided as a registration holeof the PT optical module 60.

As illustrated in FIG. 2B, the guide hole 62 is provided in the mainbody portion 61 of the PT optical module 60. The main body portion 61 isformed from, for example, epoxy resin. Further, as illustrated in FIG.2C, a printed circuit board 63 is provided inside the main body portion61, and an element 65 and a driver IC 66 are mounted on wires 64provided on the printed circuit board 63. Note that the element isconfigured from, for example, a surface-emitting laser element (verticalresonator laser, VCSEL), or a photodiode. The first member 10 as themain body portion of the PT optical connector is fastened to the mainbody portion 61 of the PT optical module 60 using a clamp spring (notillustrated).

The second member 30 can be fabricated as follows, for example.Specifically, a copper round rod is prepared, and cut into apredetermined length to provide a pellet. The pellet is placed in a moldfor the second member 30 having the columnar lower member 31 and thecolumnar upper member 34, and molded to obtain the second member 30having the columnar lower member 31 and the columnar upper member 34.The second member 30 is then placed on a support member with the mountface 32 in contact therewith, and a titanium film 35 is deposited on thewhole surface of the second member 30 except for the mount face 32 bysputtering in a sputtering apparatus.

The lower member 31 of the second member 30 is a columnar member havinga diameter of 2.00 mm (tolerance h7) and a height of 0.70 mm. The uppermember 34 is a columnar member with a diameter of 1.00 mm and a heightof 0.80 mm. Specifically, the diameter R₂ of the outer shape of themount face 32 of the second member 30 is 2.00 mm. The diameter R₁ of theouter shape of the annular aperture portion 21 is 2.00 mm, and thediameter R₁′ of the inner shape is 1.40 mm. The width of thediscontinuous portion (joint portions) 22 is 0.20 mm. Note thatR₁/R₂=1.00.

In the following, the mounting method of two members of the firstembodiment will be described with reference to the schematic partial endviews of the first member 10 (FIGS. 3A and 3B, FIG. 4A, and FIG. 5A),the partial cross sectional views (FIG. 4B, FIG. 5B), and the partialschematic plan view of the pad layer and the solder paste layer (FIG.3C). Note that, in the drawings, the center line of the aperture portion21 is denoted by CL₁, and the center line of the second member 30 byCL₂.

[Step-100]

First, a photosensitive polyimide film was laminated on portions of thefirst member 10 provided with the copper layer 12. The polyimide filmwas then exposed and developed to form the pad layer 20 having theaperture portion 21 with discontinuous portions (joint portions) 22 intwo portions. The nickel layer 13 was then formed by plating on thecopper layer 12 exposed to the bottom of the aperture portion 21. Thesecond member 30 was cleaned by successively performing ultrasonicwashing using acetone, water washing, and soft etching of the copperexposed to the mount face 32 of the second member 30.

[Step-110]

Thereafter, the aperture portion 21 was filled with the solder pastelayer 40, for which, for example, a commercially available Sn-3.0 Ag-0.5Cu material was used. Specifically, as illustrated in FIGS. 3A, 3B, and3C, the solder paste layer 40 was applied to substantially the wholesurface of the aperture portion 21 using a screen printing method. Notethat the solder paste layer 40 slightly bulged beyond the apertureportion 21 onto the edge on the pad layer 20 to form the solder pastelayer 40 thereon. However, this is not a requirement.

[Step-120]

The next step is to dispose the mount face 32 of the second member 30 onthe solder paste layer 40 (see FIGS. 4A and 4B). Specifically, thesecond member 30 was placed on the solder paste layer 40 in a mannerallowing the solder paste layer 40 to contact the mount face 32 of thesecond member 30.

[Step-130]

The solder paste layer 40 was then melted and cooled to mount the secondmember 30 on the first member 10. Specifically, the first member 10 andthe second member 30 were heated to 260° C. as a whole using a reflowmethod, so as to reflow the solder paste layer 40. This allowed thesecond member 30 to be mounted on the first member 10 by self-aligningunder the surface tension created by the melting of the solder pastelayer 40 (see FIGS. 5A and 5B). Specifically, as illustrated in FIGS. 4Aand 4B, the second member 30 moves on the solder paste layer 40 in themolten state under the surface tension created by the melting of thesolder paste layer 40, allowing the center of the second member 30 tocoincide with the center of the aperture portion 21, even when thesecond member 30 is placed on the solder paste layer 40 off-center withthe center of the aperture portion 21 in Step-120. Accordingly, theplacement of the second member 30 on the solder paste layer 40 inStep-120 does not require high accuracy. Further, because the solderpaste layer 40 has poor wettability against the pad layer 20 formed bythe photosensitive polyimide film, the solder paste layer 40 melting onthe pad layer 20, the discontinuous portions (joint portions) 22, andthe pad layer center region 24 is repelled by the pad layer 20, thediscontinuous portions 22, and the pad layer center region 24, andoccupies inside the aperture portion 21 and the space over the apertureportion 21. The solder paste layer 40 after being melted can thuscompletely fill the aperture portion 21. That is, the solder paste layer40 does not exist on the pad layer 20, the discontinuous portions 22,and the pad layer center region 24 after melting, and the discontinuousportions 22 and the pad layer center region 24 are separated from themount face 32 of the second member 30 by a gap 25. Further, because ofthe film 35 of poor solder wettability formed on the whole surface ofthe second member 30 except for the mount face 32, the solder pastelayer 40 after being melted does not adhere to the side face 33 of thesecond member 30.

For testing, member assemblies were produced in the same manner byvarying the outer shape diameter (R₁) of the annular aperture portion 21to 2.10 mm, 2.05 mm, 1.95 mm, and 1.90 mm.

Each member assembly was then measured to find the extent that thecenter of the second member 30 is off-center from the center of theaperture portion 21. The measurement results (unit: μm) are presented inthe Table 1 below. The off-center distance (Δ1 to Δ5: unit in μm) wasconfined within 5 μm in all five samples when the outer shape diametersof the annular aperture portion 21 are 2.05 mm, 2.00 mm, and 1.95 mm.Specifically, the registration accuracy was confined within 0.25%(=0.005/2.00×100). On the other hand, the off-center distance did notfall within the 5 μm range in all five samples when the outer shapediameters of the annular aperture portion 21 are 2.10 mm and 1.90 mm. Itwas therefore found that the off-center distance could be kept low when0.90<R₁/R₂<1.1. Note that even the same testing conducted for sampleswith the outer shape diameters of annular aperture portion 21 other than2.00 mm revealed that the registration accuracy for the aperture portion21 of the second member 30 could be confined within 0.25% when0.90<P₁/R₂<1.1.

TABLE 1 Δ (standard R1 Δ1 Δ2 Δ3 Δ4 Δ5 Δ (mean value) deviation) 1.90 mm13.3 4.2 18.1 7.2 4.3 9.42 6.10 1.95 mm 3.6 1.8 0.0 3.0 1.2 1.92 1.432.00 mm 0.6 3.0 1.2 3.0 1.8 1.92 1.07 2.05 mm 1.2 4.8 3.6 0.6 2.4 2.521.72 2.10 mm 3.9 2.4 12.0 0.6 0.6 3.90 4.73

In the member mounting method or the member assembly of the presentdisclosure, the annular aperture portion 21 exposing the first member 10to the bottom and having at least one discontinuous portion 22 isprovided in the pad layer 20 region for the second member 20 having themount face 32. Further, the annular aperture portion 21 has the sameouter shape as the mount face 32 of the second member 30. Thus, thesecond member 30 can self-align with the first member 10 when beingmounted on the first member 10 with the solder paste layer 40. Further,the melting of the solder paste layer 40 does not leave a gas componentat the interface between the solder paste layer 40 and the mount face 32of the second member 30, because a flux or other gas componentscontained in the solder paste layer 40 can be released to outside viathe discontinuous portions 22 formed in the annular aperture portion 21,or more specifically via the gap 25. The second member 30 can thus bemounted on the first member 10 both accurately and easily.

Further, because of the gap 25, the portion of the mount face 32 of thesecond member 30 not in contact with the solder paste layer 40 can bewashed. Further, an underfill can fill the space between this portion ofthe mount face 32 of the second member 30 and the discontinuous portions22 and the pad layer center region 24. This improves the bondingstrength of the second member 30 with the discontinuous portions 22 andthe pad layer center region 24. The underfill used herein is a sealingresin used to improve the reliability of the interconnections for an ICpackage. By being applied between the second member 30 and thediscontinuous portions 22, the underfill can easily enter the gap 25between the second member 30 and the discontinuous portions 22 and thepad layer center region 24 by capillary action.

The member mounting method and the member assembly of the presentdisclosure have been specifically described based on the preferredembodiment and example. However, the member mounting method and themember assembly of the present disclosure are not limited to theforegoing embodiment and example. The first member and the second memberdescribed in the foregoing embodiment and example are merelyillustrative, and may be varied as appropriate. For example, a PToptical module may be used as the member assembly configured from thefirst member and the second member, and a PT optical connector may beused as the component for mounting the member assembly using the secondmember for registration. Further, as the member assembly, an opticalconnector or an optical module configured or structured differently fromthose described above, for example, such as the optical connectors andoptical modules disclosed in JP-A-2011-017924, JP-A-2011-017925,JP-A-2008-046367, and JP-A-2004-184429 maybe used. Further, as the firstmember, for example, a printed board, a printed circuit board, asubstrate, a display device, or an electronic component may be used,whereas as the second member a registration pin to be mounted to variousmembers, including a printed board, a printed circuit board, asubstrate, a display device, and an electronic component may be used.

In the foregoing Example, the titanium film 35 of poor solderwettability was deposited on the side face 33 of the second member 30.However, for example, a polyimide resin layer maybe formed instead.Specifically, a polyimide resin layer may be formed on the side face 33of the second member 30 by dipping the second member 30 in a polyimideresin solution after mounting a retaining member in contact with themount face 32 of the second member 30 via a weak adhesive layer, andthen heating the polyimide resin layer formed on the whole surface ofthe second member 30 except for the mount face 32. Alternatively, thesecond member may be produced from a heat-resistant plastic material(for example, polyimide resin, or engineering plastic material) that canwithstand the melting temperature of the solder paste layer, and, forexample, a metallic layer of copper may be formed on the mount face ofthe second member.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2011-047344 filed in theJapan Patent Office on Mar. 4, 2011, the entire contents of which arehereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A method for mounting a second member on a firstmember, wherein a pad layer is provided on the first member, and whereinan annular aperture portion exposing the first member to the bottom andhaving at least one discontinuous portion is provided in a region of thepad layer for mounting the second member having a mount face, theannular aperture portion having the same outer shape as the mount faceof the second member, the method comprising: filling the apertureportion with a solder paste layer; and disposing the mount face of thesecond member on the solder paste layer, and melting and cooling thesolder paste layer to mount the second member on the first member. 2.The method according to claim 1, wherein the second member has a sideface that extends from the mount face, and is formed from copper, acopper alloy, an aluminum, or an aluminum alloy, and wherein a film ofpoor solder wettability is formed on the side face of the second member.3. The method according to claim 1, wherein the solder paste layer ismelted after disposing the mount face of the second member on the solderpaste layer, so as to mount the second member on the first member byallowing the second member to self-align under the surface tensioncreated by the melting of the solder paste layer.
 4. The methodaccording to claim 1, wherein 0.90<P₁/R₂<1.1 is satisfied, where R₁ isthe diameter of the outer shape of the annular aperture portion, and R₂is the diameter of the outer shape of the mount face of the secondmember.
 5. The method according to claim 1, wherein the annular apertureportion has N discontinuous portions (where N is a natural number of 2or more), and the N discontinuous portions are disposed with N-foldrotational symmetry.
 6. The method according to claim 1, wherein theouter shape of the annular aperture portion is circular.
 7. The methodaccording to claim 1, wherein the first member in the portion exposed tothe bottom of the aperture portion is formed by a copper layer and anickel layer formed on the copper layer.
 8. The method according toclaim 1, wherein the mount face of the second member is configured fromcopper, a copper alloy, aluminum, or an aluminum alloy.
 9. A memberassembly comprising: a first member that includes a pad layer; a secondmember that has a mount face; an annular aperture portion provided in asecond member-mounting region of the pad layer so as to expose the firstmember to the bottom and form at least one discontinuous portion,wherein the annular aperture portion has the same outer shape as themount face of the second member; and a solder paste layer filling theaperture portion to mount the second member on the first member.
 10. Themember assembly according to claim 9, wherein the second member has aside face that extends from the mount face, and is formed from copper, acopper alloy, aluminum, or an aluminum alloy, and wherein a film of poorsolder wettability is formed on the side face of the second member. 11.The member assembly according to claim 9, wherein 0.90<R₁/R₂<1.1 issatisfied, where R₁ is the diameter of the outer shape of the annularaperture portion, and R₂ is the diameter of the outer shape of the mountface of the second member.
 12. The member assembly according to claim 9,wherein the annular aperture portion has N discontinuous portions (whereN is a natural number of 2 or more), and wherein the N discontinuousportions are disposed with N rotational symmetry.
 13. The memberassembly according to claim 9, wherein the outer shape of the annularaperture portion is circular.
 14. The member assembly according to claim9, wherein the first member in the portion exposed to the bottom of theaperture portion is formed by a copper layer and a nickel layer formedon the copper layer.
 15. The member assembly according to claim 9,wherein the mount face of the second member is configured from copper, acopper alloy, aluminum, or an aluminum alloy.